This invention concerns an internal combustion engine with at least one exhaust valve and more than one inlet valve per cylinder, as well as a mechanism for operating the valves separately.
The power of a combustion engine rises with an increase in cylinder capacity and revolutions per minute (rpm). However, with a large capacity, the oscillating mass of the big pistons limits high rpm. Therefore, high powered engines use multiple, smaller cylinders designed for high rpm, but subsequently suffer a loss of torque at lower rpm.
For an elastic engine characteristic with strong torque the intake ports are narrow and long, whereas for maximum power they should be relatively short and wide. In order to optimize the gas exchange in the cylinder for the best engine performance at high and low rpm, several solutions have been proposed with limited success, such as variable length intake ports, the semi-closure of a double barrel carburetor or the disengagement of the valve lifters at partial power loads.
Another proposal on this subject is the variable valve timing with which at different rpm the valve lift time and height can be regulated, thus changing the valve overlapping timings. Overlapping timings between the exhaust valve closure and the inlet valve opening have been standard engineering for a long time, whereby the mass of the escaping exhaust gas column generates a tiny vacuum in the exhaust port. As the inlet valve is opened early, this vacuum sucks the slightly pressurized fresh gas column into movement, resulting in an overall higher cylinder filling grade. The longer the distance between the exhaust valve and the inlet valve, the earlier the inlet valve can be opened without fresh gas escaping through the exhaust port. This circumstance has not yet been exploited to the fullest in multivalve engines.
The overlapping times of existing multivalve engines are very short because the synchronously opening inlet valves are close to the opposite facing exhaust valves. The advantage lies in the smaller size of the valves which are therefore lighter, enabling higher rpm. Also the circumference of multiple valves is bigger than with a single, even larger valve, enabling a higher gasflow. A single inlet valve engine has the advantage that through placing the valve out of the center of the cylinder axis, a very desirable, unidirectional whirl is created by the inflowing gas, resulting in a higher filling grade and a quicker, smoother burn of the gas. This advantage is lost with multivalve engines because gas flowing through the side-by-side valves tends to form a rolling collision turbulence, causing slower and irregular burn patterns at various, especially high rpm, resulting in spontaneous detonation. A desirable unidirectional whirl can be achieved with multivalve engines at partial power when one of the intake ports is closed; but as soon as the adjacent port is opened for power increase, the whirl collapses and changes into an aforesaid collision turbulence.
Furthermore, present high performance use long valve shafts order to direct the intake ports as straight as possible to the inlet valves so that the gas flows at a steep angle past the valve evenly around the opening gap. However, this induces a small vortex beneath each valve which again disturbs the desirably even swirl within the cylider. Furthermore, with longer valve shafts the oscillating mass rises, which is contrary to the aim of attaining high rpm.